Method and apparatus for monitoring battery status of implantable medical device

ABSTRACT

A battery monitoring system monitors status of a battery in an implantable medical device by comparing a measured battery status trend to a calculated battery status trend. The measured battery status trend is a trend of measured parameter values each indicative of an actual state of depletion of the battery. The calculated battery status trend is a trend of calculated parameter values each indicative of an expected state of depletion of the battery.

TECHNICAL FIELD

This document relates generally to implantable medical devices andparticularly to monitoring battery status of an implantable medicaldevice.

BACKGROUND

Medical devices are implanted in human bodies for monitoringphysiological conditions, diagnosing diseases, treating diseases, orrestoring functions of organs or tissues. Examples of such implantablemedical devices include cardiac rhythm management (CRM) devices, neuralstimulators, neuromuscular stimulators, drug delivery devices, andbiological therapy devices. One particular example of implantablemedical devices is a CRM device implanted in a patient to treatirregular or other abnormal cardiac rhythms by delivering electricalpulses to the patient's heart. Such rhythms result in diminished bloodcirculation. Examples of implantable CRM devices include pacemakers anddefibrillators. Pacemakers are often used to treat patients withbradyarrhythmias, that is, hearts that beat too slowly or irregularly.Such pacemakers may coordinate atrial and ventricular contractions toimprove the heart's pumping efficiency. Defibrillators are capable ofdelivering higher energy electrical stimuli to the heart. Suchdefibrillators may also include cardioverters, which synchronize thedelivery of such stimuli to portions of sensed intrinsic heart activitysignals. Defibrillators are often used to treat patients withtachyarrhythmias, that is, hearts that beat too quickly. In addition topacemakers and defibrillators, implantable CRM systems also include,among other things, pacer/defibrillators that combine the functions ofpacemakers and defibrillators, drug delivery devices, and any otherimplantable systems or devices for diagnosing or treating cardiacarrhythmias.

Batteries are used as energy sources for implantable medical devices.While the use of battery allows a medical device to be totallyimplantable, without the need of transcutaneous power transmission, thepower consumption and the longevity of the medical device is limited bythe capacity of the battery. For example, most treatments usingimplantable CRM devices are long-term treatments that may last up to thepatient's lifetime. When the battery of an implantable CRM device is nolonger able to provide sufficient energy for the operation of thedevice, the device is to be explanted and replaced. Thus, for patientsafety and device longevity, among other reasons, there is a need formonitoring the status of a battery in an implantable medical device.

SUMMARY

A battery monitoring system monitors the status of a battery in animplantable medical device by comparing a measured battery status trendto a calculated battery status trend. The measured battery status trendis a trend of measured parameter values each indicative of an actualstate of depletion of the battery. The calculated battery status trendis a trend of calculated parameter values each indicative of an expectedstate of depletion of the battery.

In one embodiment, a system for monitoring status of a battery in animplantable medical device includes a battery analyzer. The batteryanalyzer includes a parameter input and a trending module. The parameterinput receives measured values of a battery functional parameter andcalculated values of the battery functional parameter. The batteryfunctional parameter is indicative of a state of depletion of thebattery. The measured values are each indicative of an actual state ofdepletion of the battery. The calculated values are each indicative ofan expected state of depletion of the battery. The trending moduleproduces a measured battery status trend being a trend of the measuredvalues of the battery functional parameter and a calculated batterystatus trend being a trend of the calculated values of the batteryfunctional parameter.

In one embodiment, a method for monitoring status of a battery in animplantable medical device is provided. Values of a battery functionalparameter indicative of a state of depletion of the battery aremeasured. The measured values are each indicative of an actual state ofdepletion of the battery. Values of the battery functional parameter areeach calculated as a function of one or more specification parameters ofthe battery and one or more consumption parameters indicative of energyconsumption from the battery. The calculated values are each indicativeof an expected state of depletion of the battery. A measured batterystatus trend being a trend of the measured values of the batteryfunctional parameter and a calculated battery status trend being a trendof the calculated values of the battery functional parameter.

This Summary is an overview of some of the teachings of the presentapplication and not intended to be an exclusive or exhaustive treatmentof the present subject matter. Further details about the present subjectmatter are found in the detailed description and appended claims. Thescope of the present invention is defined by the appended claims andtheir legal equivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate generally, by way of example, variousembodiments discussed in the present document.

FIG. 1 is an illustration of an embodiment of a system including animplantable medical device and an external system and portions of anenvironment in which the system is used.

FIG. 2 is a block diagram illustrating an embodiment of circuits of theimplantable medical device and the external system.

FIG. 3 is a block diagram illustrating an embodiment of the externalsystem.

FIG. 4 is a block diagram illustrating an embodiment of a batteryanalyzer.

FIG. 5 is an illustration of an embodiment of a trending process showingits inputs and outputs.

FIG. 6 is a graph illustrating a measured battery status trend and acalculated battery status trend.

FIG. 7 is a block diagram illustrating an embodiment of a batterymonitoring system including the battery analyzer.

FIG. 8 is a block diagram illustrating an embodiment of distribution ofthe battery monitoring system in the implantable medical device and theexternal system.

FIG. 9 is a block diagram illustrating another embodiment ofdistribution of the battery monitoring system in the implantable medicaldevice and the external system.

FIG. 10 is a flow chart illustrating an embodiment of a method formonitoring status of a battery in an implantable medical device.

FIG. 11 is a flow chart illustrating another embodiment of a method formonitoring status of the battery in the implantable medical device.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings which form a part hereof, and in which is shown byway of illustration specific embodiments in which the invention may bepracticed. These embodiments are described in sufficient detail toenable those skilled in the art to practice the invention, and it is tobe understood that the embodiments may be combined, or that otherembodiments may be utilized and that structural, logical and electricalchanges may be made without departing from the spirit and scope of thepresent invention. References to “an”, “one”, or “various” embodimentsin this disclosure are not necessarily to the same embodiment, and suchreferences contemplate more than one embodiment. The following detaileddescription provides examples, and the scope of the present invention isdefined by the appended claims and their legal equivalents.

This document discusses a battery monitoring system for monitoringstatus of a battery in an implantable medical device. The systemmeasures values of a battery functional parameter, produces a measuredbattery status trend being a trend of the measured values of the batteryfunctional parameter, calculates values of the battery functionalparameter, and produces a calculated battery status trend being a trendof the calculated values of the battery functional parameter. Thebattery functional parameter is indicative of a state of depletion ofthe battery. Each measured value of the battery functional parameter isindicative of an actual state of depletion of the battery. Eachcalculated value of the battery functional parameter is indicative of anexpected (or projected) state of depletion of the battery. The state ofdepletion of the battery is indicative of the remaining life of thebattery. In various embodiments, one or more battery functionalparameters are measured, calculated, and trended. In one embodiment, ameasured battery status trend and a calculated battery status trend areproduced for each battery functional parameter. In another embodiment, ameasured battery status trend and a calculated battery status trend areproduced for a parameter that is a function of a plurality of batteryfunctional parameters.

The system monitors the depletion of the battery by using the measuredbattery status trend and the calculated battery status trend. In variousembodiments, measured values of the battery functional parameters orvalues of the battery functional parameters taken from the measuredbattery status trend are compared to the calculated battery statustrend. The difference between the actual state of depletion and theexpected state of depletion is used to indicate, for example, adequacyof implantable medical device programming, performance of theimplantable medical device, and/or remaining life of the battery (whichin turn indicates a need to replace the implantable medical device).

FIG. 1 is an illustration of an embodiment of a system 100 and portionsof an environment in which system 100 is used. System 100 includes animplantable medical device 110, a lead system 108, and an externalsystem 190. A wireless telemetry link 180 provides for communicationbetween implantable medical device 110 and external system 190.Implantable medical device 110 is a battery-powered device. A batterymonitoring system 120, including portions 120A in implantable medicaldevice 110 and portions 120B in external system 190, providesimplantable medical device 110 with battery monitoring. While a CRMsystem, as shown in FIG. 1, is discussed as a specific example, thepresent subject matter applies to any system that includes one or morebattery-powered implantable medical devices.

After implantation, implantable medical device 110 operates within abody 102 of a patient to sense activities of a heart 105 and deliver oneor more therapies to heart 105 through lead system 108. In oneembodiment, as illustrated in FIG. 1, implantable medical device 110 isan implantable CRM device that delivers one or more therapies including,but are not limited to, a pacing therapy, a cardioversion/defibrillationtherapy, a cardiac resynchronization therapy (CRT), a remodeling controltherapy (RCT), a drug therapy, and a biological therapy such as a celltherapy and a gene therapy.

Lead system 108 provides one or more electrical connections betweenimplantable medical device 110 and heart 105. In one embodiment, leadsystem 108 includes one ore more leads each including one or moreelectrodes configured for endocardial and/or epicardial placement.Pacing and/or cardioversion/defibrillation are delivered to heart 105through such leads and electrodes. In one embodiment, one or more leadsof lead system 108 also include agent delivery ports configured forendocardial, epicardial, and/or intravascular placement. Substances suchas chemical or biological agents are delivered to heart 105 through suchleads and agent delivery ports.

External system 190 communicates with implantable medical device 110 viatelemetry link 180. In one embodiment, external system 190 includes anexternal programmner. In another embodiment, external system 190includes a portable device, such as a hand-held device, provided for useby the patient or another person providing care to the patient. Inanother embodiment, external system 190 includes a patient managementsystem including an external device communicating with implantablemedical device 110 via telemetry link 180, a network coupled to theexternal device, and a remote device coupled to the network. Such apatient management system allows a physician or other caregiver tocommunicate with implantable medical device 110 through the remotedevice in a distant location.

Telemetry link 180 provides for data transmission between implantablemedical device 110 and external system 190. Data transmission fromimplantable medical devices 110 to external system 190 includes, forexample, transmitting real-time physiological data acquired byimplantable medical devices 110, extracting physiological data acquiredby and stored in implantable medical devices 110, extracting therapyhistory data stored in implantable medical devices 110, and extractingdata indicating an operational status of implantable medical devices,such as battery status and lead impedance. Data transmission fromexternal system 190 to implantable medical devices 110 includes, forexample, programming implantable medical devices 110 to acquirephysiological data, programming implantable medical devices 110 toperform at least one self-diagnostic test (such as for a battery statusand lead impedance status), programming implantable medical devices 110to perform a diagnostic task, and programming implantable medicaldevices 110 to deliver a therapy.

Battery monitoring system 120 monitors the status of one or morebatteries in implantable medical device 110 by comparing the measuredvalues of a battery functional parameter or a measured battery statustrend to a corresponding calculated battery status trend to determinewhether the actually state of depletion substantially deviates from atheoretically projected state of depletion. The result is used toindicate, for example, a need for reprogramming implantable medicaldevice 110 to lower its power consumption and/or a need for replacingimplantable medical device 110.

FIG. 2 is a block diagram illustrating an embodiment of circuits of animplantable medical device 210 and an external system 290. Implantablemedical device 210 represents an embodiment of implantable medicaldevice 110 and includes a feature circuit 222, an implant telemetrycircuit 224, and a power source 230. External system 290 represents anembodiment of external system 190 and includes an external telemetrycircuit 236, an external battery monitoring circuit 238, and a userinterface 240. Telemetry link 180 provides for data transmission betweenimplantable medical device 210 and external system 290.

Feature circuit 222 performs one or more of sensing, diagnostic, andtherapeutic functions. In one embodiment, as illustrated in FIG. 2,feature circuit 222 includes an electrical stimulation circuit 226 and asensing circuit 228. Electrical stimulation circuit 226 deliverselectrical stimulation to body 102. Examples of electrical stimulationcircuit 226 include a pacing circuit that delivers pacing pulses, acardioversion/defibrillation circuit that deliverscardioversion/defibrillation pulses, and a neural stimulation circuitthat delivers neural stimulation pulses. Sensing circuit 228 senses oneor more physiological signals such as electrograms, heart sounds orsignals indicative of heart sounds, activity level signals, pressuresignals, impedance signals, and respiratory signals. In variousembodiments, feature circuit 222 includes one or more of electricalstimulation circuit 226, sensing circuit 228, a diagnostic circuit toperform one or more diagnostic functions using the one or morephysiological signals sensed by sensing circuit 228, a drug deliverydevice to deliver one or more pharmaceutical agents, and a biologicaltherapy device to deliver one or more biologic therapies.

Power source 230 includes a battery 232 and an implant batterymonitoring circuit 234. Battery 232 represents one or more batterieshoused in implantable medical device 210 to provide energy for itsoperation, including energy delivered to body 102 for therapeuticpurposes. Examples of battery 232 include lithium manganese dioxide andlithium carbon monofluoride batteries. In one embodiment, battery 232includes one or more rechargeable batteries such as rechargeable lithiumand lithium ion batteries, in addition to or in place of one or morenon-rechargeable batteries.

Implant telemetry circuit 224 receives signals from external system 290and transmits signals to external system 290 via telemetry link 180. Inone embodiment, implant telemetry circuit 224 also allows forcommunication between implantable medial device 210 and one or moreother implantable medical devices implanted in body 102. Externaltelemetry circuit 236 transmits signals to implantable medial device 210and receives signals transmitted from implantable medical device 210 viatelemetry link 180.

Implant battery monitoring circuit 234 and external battery monitoringcircuit 238 include battery monitoring system 120. In variousembodiments, components of battery monitoring system 120 are distributedin implantable medical device 210 and external system 290. Examples ofthis distribution are discussed below, with reference to FIGS. 7 and 8.

User interface 240 allows a user such as the physician or othercaregiver or the patient to communicate with implantable medical device210. User interface 240 includes a user input device 242 and apresentation device 244. User input device 242 receives information suchas commands and parameters from the user. Presentation device 244informs the user of the status of the patient, implantable medicaldevice 210, and external system 290. In the illustrated embodiment,presentation device 244 includes a screen 246, a printer 248, and analarm device 250. For example, information representative of the statusof battery 232 acquired by battery monitoring system 120, including themeasured and calculated battery status trends, are displayed on screen246 and/or printed on printer 248. If battery monitoring system 120detects an alerting event, such as an abnormally high power consumptionor low energy level indicating a need for battery replacement, alarmdevice 250 produces an alarm signal such as an audio tone or a textualmessage. In response, the user determines whether there is a need toreplace implantable medical device 210 or to reprogram therapyparameters used by feature circuit 222. For example, abnormally highpower consumption may be caused by inappropriate device setting orhigher-than expected use of therapeutic energy due to physiology of aparticular patient. In such cases, the power consumption may be loweredby reprogramming implantable medical device 210 with adequate therapyparameters and/or an alternative therapy strategy. On the other hand, anabnormally high power consumption caused by device failure usuallyrequires replacement of implantable medical device 210.

FIG. 3 is a block diagram illustrating an embodiment of an externalsystem 390, which represents an embodiment of the distribution ofexternal system 190. As illustrated in FIG. 3, external system 390 is apatient management system including an external device 392, atelecommunication network 394, and a remote device 396. External device394 is placed within the vicinity of implantable medical device 190 andincludes external telemetry circuit 236 to communicate with implantablemedical device 190 via telemetry link 180. Remote device 396 is in aremote location and communicates with external device 392 throughnetwork 394, thus allowing the user to monitor and treat a patient froma distant location and/or allowing access to various treatment resourcesfrom the remote location. Remote device 396 includes user interface 240,or at least a portion of user interface 240, and allows the user tomonitor the battery of implantable medical device 110 through batterymonitoring system 120. In one embodiment, external system 390 allows formonitoring of batteries in multiple implantable medical devices,including statistical analysis using data acquired from multipleimplantable medical devices to indicate battery usage and performance inthese devices.

FIG. 4 is a block diagram illustrating an embodiment of a batteryanalyzer 452 of battery monitoring system 120. Battery analyzer 452includes a trending module 454. Trending module 454 includes a parameterinput 456 and a processing circuit 458. Parameter input 456 receivesmeasured values of a battery functional parameter and calculated valuesof the battery functional parameter. The battery functional parameterindicates the remaining energy in a battery relative to the fullcapacity of the battery. The measured values are each measured frombattery 232 and each indicate an actual state of depletion of battery232. The calculated values are each calculated using a predeterminedformula with known parameters such as battery specification parametersand therapy energy consumption and each indicate an expected state ofdepletion of battery 232. Processing circuit 458 produces a measuredbattery status trend and a calculated battery status trend. The measuredbattery status trend is a trend of the measured values of the batteryfunctional parameter. The calculated battery status trend is a trend ofthe calculated values of the battery functional parameter.

In various embodiments, instructions for producing the measured batterystatus trend and the calculated battery status trend are stored in astorage device coupled to or included in processing circuit 458 and in aform that is readable and executable by processing circuit 458. In oneembodiment, processing circuit 458 includes portions of amicroprocessor, such as a microprocessor of implantable medical device110 or 210, configured to execute the instructions for producing themeasured battery status trend and the calculated battery status trend.In another embodiment, processing circuit 458 includes portions of amicroprocessor or other processing circuit of a computer or computerizeddevice, such as a computer or computerized device of external system 190or 290, configured to execute instructions for producing the measuredbattery status trend and the calculated battery status trend.

FIG. 5 is an illustration of an embodiment of a trending process showingits inputs and outputs. In one embodiment, the trending process isperformed using processing circuit 458 for a battery in an implantablemedical device. In the illustrated embodiment, the inputs include aterminal voltage being a voltage across two terminals of the battery, acharging time being a time interval during which a capacitor in theimplantable medical device (such as a defibrillation capacitor) ischarged to a specified energy level using the battery, a chargedepletion parameter indicative of a cumulative charge depleted from thebattery, specification parameters (“factory parameters”) of the battery,length of use (i.e., length of time since implantation of theimplantable medical device), programmed device parameters of theimplantable medical device, and measured device parameters of theimplantable medical device. The outputs include the measured and thecalculated battery status trends and parameters and indicators derivedfrom these trends, including the remaining energy of the battery, aprojected remaining life of the battery, an elective replacementindicator (ERI), an end-of-life (EOL) indicator, and a high currentdrain alarm signal. In various embodiments, the inputs of the trendingprocess include any one or more inputs selected from those illustratedin FIG. 5 and additional inputs suitable for use in the battery statustrending, and the outputs of trending process include any one or moreoutputs selected from those illustrated in FIG. 5 and additional outputsfor battery monitoring. An example of a system that performs thetrending process is further discussed below, with reference to FIG. 7.

FIG. 6 is a graph illustrating a measured battery status trend 610 and acalculated battery status trend 600. Measured battery status trend 610represents a specific example for the measured battery status trendproduced by processing circuit 458. Calculated battery status trend 600represents a specific example of the calculated battery status trendproduced by processing circuit 458. The state of depletion isrepresented by the remaining capacity of battery 232 as a percentage thefull capacity of battery 232. As illustrated in FIG. 6, measured batterystatus trend 610 deviates from calculated battery status trend 600 by adifference δ. In various embodiments, the difference δ is used as anindication of whether the usage and performance of battery 232 is withina normal range. A difference δ that is outside the normal rangeindicates a need for user intervention, such as to preserve thelongevity of implantable medical device 110. Additionally, measuredbattery status trend 610 and calculated battery status trend 600 providefor an indication when battery 232 is near its end of life, whichrequires replacement of implantable medical device 110.

FIG. 7 is a block diagram illustrating an embodiment of a batterymonitoring system 720, which represents an embodiment of batterymonitoring system 120. Battery monitoring system 720 includes a batteryparameter monitor 762, a battery parameter calculator 766, and a batteryanalyzer 752. In the illustrated embodiment, battery monitoring system720 includes a trending module and its peripheral devices to perform thetrending process discussed above with reference to FIG. 5.

Battery parameter monitor 762 measures the values of one or more batteryfunctional parameters indicative of the state of depletion of battery232. In the illustrated embodiment, battery parameter monitor 762includes a terminal voltage monitor 763, a charging time monitor 764,and a charge depletion monitor 765. In various other embodiments,battery parameter monitor 762 includes any one or more of terminalvoltage monitor 763, charging time monitor 764, and charge depletionmonitor 765, depending on the battery functional parameter(s) selectedfor trending. Terminal voltage monitor 763 measures a terminal voltagebeing the voltage across two terminals of battery 232. Charging timemonitor 764 measures a capacitor charging time being a time intervalduring which a capacitor in implantable medical device 110 (such as adefibrillation capacitor) is charged to a specified energy level usingbattery 232. Charge depletion monitor 765 measures a charge depletionparameter indicative of a cumulative charge depleted from battery 232.An example of measuring the charge depletion parameter is discussed inU.S. patent application Ser. No. 10/706,856, entitled “SYSTEM AND METHODFOR MONITORING OR REPORTING BATTERY STATUS OF IMPLANTABLE MEDICALDEVICE”, filed on Nov. 12, 2003, assigned to Cardiac Pacemakers, Inc.,which is incorporated herein by reference in its entirety.

Battery parameter calculator 766 calculates the value of the one or morebattery functional parameters and includes a specification parameterregister 767, a consumption parameter register 768, and a calculator769. Specification parameter register 767 stores specificationparameters including the “factory parameters” specified for battery 232.Consumption parameter input 768 receives and stores consumptionparameters including various parameters indicative of or contributing tothe energy consumed from battery 232. Calculator 769 produces the valuesof the battery functional parameter each as a function of one or morespecification parameters and one or more consumption parameters. Thecalculated values each represent a theoretical expectation for the stateof depletion of battery 232 based on the built-in characteristics ofbattery 232 and how it is expected to be used. An example of aspecification parameter includes the battery capacity specified forbattery 232. Examples of the consumption parameters include the lengthof time since implantation of implantable medical device 110, programmeddevice parameters such as parameters controlling delivery of therapeuticenergy from implantable medical device 110 (such as programmed pacingand defibrillation parameters), measured device parameters (such asimpedance of each lead in lead system 108), and operation historyparameters indicative of energy consumed from battery 232 (such asnumber of defibrillation shocks delivered since device implantation).

Battery analyzer 752 is a specific embodiment of battery analyzer 452and includes a trending module 754, a trend alarm 770, and a remaininglife indicator 772. Trending module 754 includes a parameter input 756and a processing circuit 758. Parameter input 756 receives parametersincluding the inputs to processing circuit 758. Processing circuit 758represents an embodiment of processing circuit 458 and produces themeasured battery status trend and the calculated battery status trendusing the parameters received by parameter 554. In one embodiment,processing circuit 758 produces a measured battery status trend and acorresponding calculated battery status trend for one battery functionalparameter. In another embodiment, processing circuit 758 produces ameasured battery status trend and a corresponding calculated batterystatus trend for each of a plurality of battery functional parameters.In another embodiment, processing circuit 758 produces a measuredbattery status trend and a corresponding calculated battery status trendfor a battery parameter being a function of a plurality of batteryfunctional parameters. In one embodiment, trending module 754 updatesthe measured battery status trend and the calculated battery statustrend periodically, such as on a daily basis. This includes receivingthe currently measured values of the battery functional parameter,receiving the currently calculated values of the battery functionalparameter, updating the measured battery status trend, and updating thecalculated battery status trend on the period basis. The measuredbattery status trend and the calculated battery status trend arepresented using presentation device 244 periodically or upon request bythe user.

Trend alarm 770 produces an alert signal using the measured batterystatus trend and the calculated battery status trend, or using a rate ofchange in the measured battery status trend and a rate of change in thecalculated battery status trend. In one embodiment, trend alarm 770produces the alert signal when the measured battery status trenddeviates from the calculated battery status trend by at least aspecified performance margin (i.e., when δ exceeds the predeterminedperformance margin) for a monitoring period. In another embodiment,trend alarm 770 produces the alert signal when a derivative of themeasured battery status trend deviates from a derivative of thecalculated battery status trend by at least a specified performance ratemargin for the monitoring period. Remaining life indicator 772 producesthe battery life parameter using the measured battery status trend andthe calculated battery status trend. The measured battery status trendindicates the battery usage in the past, and the calculated batterystatus trend indicates projected battery usage in the future. In oneembodiment, remaining life indicator produces the ERI and/or the EOLindicator for battery 232 using the battery life parameter. Suchindicators are presented using presentation device 244 to inform the useof the need for replacement of battery 232 (typically requiringreplacement of implantable medical device 110 that is powered by battery232).

FIG. 8 is a block diagram illustrating an embodiment of a batterymonitoring system 820, which represents an embodiment of distribution ofbattery monitoring system 720 in an implant medical device and anexternal system. An implant battery monitoring circuit 834 represents anembodiment of implant battery monitoring circuit 234 and includesbattery parameter monitor 762. An external battery monitoring circuit838 represents an embodiment of external battery monitoring circuit 238and includes battery parameter calculator 766 and battery analyzer 752.

Battery monitoring system 820 allows for analysis of battery statususing information from a plurality of implantable medical devices. Inone embodiment, parameter input 456 receives the measured and/orcalculated values of the battery functional parameter for a plurality ofimplantable medical devices. Battery parameter calculator 766 adjuststhe calculated value of the battery functional parameter using themeasured and/or calculated values of the battery functional parameterfrom the plurality of implantable medical devices. Trend alarm 770produces the specified performance margin using the measured and/orcalculated values of the plurality of implantable medical devices.Remaining life indicator 772 calculates the battery life parameter foreach of the implantable medical devices using the measured and/orcalculated values of the plurality of implantable medical devices.

FIG. 9 is a block diagram illustrating an embodiment of a batterymonitoring system 920, which represents another embodiment ofdistribution of battery monitoring system 720 in an implant medicaldevice and an external system. An implant battery monitoring circuit 934represents another embodiment of implant battery monitoring circuit 234and includes battery parameter monitor 762, battery parameter calculator766, and a battery analyzer 952A. An external battery monitoring circuit938 represents another embodiment of external battery monitoring circuit238 and includes a battery analyzer 952B. Battery analyzer 952Arepresents portions of battery analyzer 752 distributed in theimplantable medical device. Battery analyzer 952B represents portions ofbattery analyzer 752 distributed in the external system. Batterymonitoring system 920 allows for battery status monitoring whilecommunication between the implantable medical device and the externalsystem is not established.

FIG. 10 is a flow chart illustrating an embodiment of a method 1000 formonitoring status of a battery in an implantable medical device. In oneembodiment, method 1000 is performed by system 100, including itsvarious embodiments discussed above.

Values of one or more battery functional parameters are measured at1010. The battery functional parameter is indicative of a state ofdepletion of the battery. The measured values are each indicative of anactual state of depletion of the battery. Examples of the one or morebattery functional parameters include a terminal voltage being a voltageacross two terminals of the battery, a capacitor charging time being atime interval during which a capacitor in the implantable medical deviceis charged to a specified energy level using the battery, and a chargedepletion parameter indicative of a cumulative charge depleted from thebattery. An example of measuring the charge depletion parameter isdiscussed in U.S. patent application Ser. No. 10/706,856.

Values of the one or more battery functional parameter are calculated at1020. The calculated values are each indicative of an expected state ofdepletion of the battery and is a function of one or more specificationparameters of the battery and one or more parameters indicative ofenergy consumption from the battery. In various embodiments, thecalculated values of the one or more battery functional parameters areproduced using parameters such as battery capacity, length of time sinceimplantation of the implantable medical device, programmed and/ormeasured device parameters affecting the energy consumption from thebattery, measured device parameters, and/or operation history parametersindicative of energy consumed from the battery. In one embodiment, thevalues of the one or more battery functional parameter is calculated at1020 as a function of one or more specification parameters of thebattery, one or more parameters indicative of energy consumption fromthe battery, and the measured and/or calculated values of the batteryfunctional parameter for a plurality of implantable medical devices.

A measured battery status trend and a calculated battery status trendare produced at 1030. The measured battery status trend is a trend ofthe measured values of the one or more battery functional parameters.The calculated battery status trend is a trend of the calculated valuesof the one or more battery functional parameters. In one embodiment, themeasured and calculated battery status trends are updated periodically,such as on a daily basis. The measured battery status trend and thecalculated battery status trend are presented to a user such as aphysician or other caregiver using a screen or printer. In variousembodiments, one or more of the terminal voltage, the capacitor chargingtime, and the charge depletion parameter are measured at 1010,calculated at 1020, and trended at 1030.

FIG. 11 is a flow chart illustrating an embodiment of a method 1100,which represents a further embodiment of method 1000. In one embodiment,method 1100 is performed by system 100, including its variousembodiments discussed above. Method 1100 starts with method 1000. Thatis, values of one or more battery functional parameter are measured at1010, values of the one or more battery functional parameter arecalculated at 1020, and a measured battery status trend and a calculatedbattery status trend are produced at 1030.

If the measured battery status trend is substantially different from thecalculated battery status trend at 1140, an alert signal is produced at1170. In one embodiment, the alert signal is produced at 1140 when themeasured battery status trend deviates from the calculated batterystatus trend by at least a specified performance margin for a monitoringperiod. In another embodiment, the alert signal is produced at 1140 whena derivative of the measured battery status trend deviates from aderivative of the calculated battery status trend by at least aspecified performance rate margin for the monitoring period. In oneembodiment, in response to the alert signal, an alarm signal, such as anaudio tone, a visual warning signal, or a textual message, is producedto notify the user. In one embodiment, the performance margin isadjusted using the measured and/or calculated values of the batteryfunctional parameter for the plurality of implantable medical devices.

A battery life parameter is produced at 1150, using the measured batterystatus trend and the calculated battery status trend. The battery lifeparameter represents an estimated remaining life expectancy of thebattery. In one embodiment, the battery life parameter is produced forthe implantable medical device using the measured and/or calculatedvalues of the battery functional parameter for the plurality ofimplantable medical devices. If the battery life parameter indicatesthat the battery is near its end of life at 1160, the alert signal isproduced at 1170 to notify the user. In one embodiment, this includesgenerating an ERI and/or an EOL using the battery life parameter topresent to the user.

It is to be understood that the above detailed description is intendedto be illustrative, and not restrictive. The scope of the inventionshould, therefore, be determined with reference to the appended claims,along with the full scope of equivalents to which such claims areentitled.

1. A system for monitoring status of a battery in an implantable medicaldevice, the system comprising: a battery analyzer configured to analyzethe status of the battery, the battery analyzer including a trendingmodule including: a parameter input configured to receive measuredvalues of a battery functional parameter and calculated values of thebattery functional parameter, the battery functional parameterindicative of a state of depletion of the battery and including at leasta terminal voltage being a voltage across terminals of the battery, themeasured values each indicative of an actual state of depletion of thebattery, the calculated values each indicative of an expected state ofdepletion of the battery; and a processing circuit configured to producea measured battery status trend being a trend of the measured values ofthe battery functional parameter and a calculated battery status trendbeing a trend of the calculated values of the battery functionalparameter.
 2. The system of claim 1, wherein the trending module isconfigured to update the measured battery status trend and thecalculated battery status trend on a periodic basis.
 3. The system ofclaim 1, wherein the battery analyzer comprises a trend alarm coupled tothe trending module and configured to produce an alert signal when themeasured battery status trend deviates from the calculated batterystatus trend by at least a specified performance margin for a monitoringperiod.
 4. The system of claim 3, wherein the trend alarm is configuredto produce the alert signal when a rate of change of the measuredbattery status trend deviates from a rate of change of the calculatedbattery status trend by at least a specified performance rate margin forthe monitoring period.
 5. The system of claim 1, wherein the batteryanalyzer comprises a remaining life indicator coupled to the trendingmodule and configured to produce a battery life parameter representingan estimated remaining life expectancy of the battery using the measuredbattery status trend and the calculated battery status trend.
 6. Thesystem of claim 1, comprising: a battery parameter monitor configured tomeasure the battery functional parameter and produce the measured valuesof the battery functional parameter, the battery parameter monitorincluding at least a terminal voltage monitor configured to measure theterminal voltage; and a battery parameter calculator configured toproduce the calculated values of the battery functional parameter eachas a function of one or more specification parameters of the battery andone or more consumption parameters indicative of energy consumption fromthe battery.
 7. The system of claim 6, wherein the battery parametermonitor further comprises a charging time monitor configured to measurea capacitor charging time being a time interval during which a capacitorin the implantable medical device is charged to a specified energy levelusing the battery.
 8. The system of claim 6, wherein the batteryparameter monitor further comprises a charge depletion monitorconfigured to produce a charge depletion parameter indicative of acumulative charge depleted from the battery.
 9. The system of claim 6,wherein the battery parameter calculator is configured to calculate thevalues of the battery functional parameter each as a function of one ormore of a specified battery capacity, a length of time sinceimplantation of the implantable medical device, stimulation parametersaffecting the energy consumption from the battery, and operation historyparameters indicative of energy consumed from the battery.
 10. Thesystem of claim 6, wherein the implantable medical device comprises animplant battery monitoring circuit coupled to the battery, and furthercomprising an external system communicatively coupled to the implantablemedical device and including an external battery monitoring circuit,wherein one or more of the implant battery monitoring circuit and theexternal battery monitoring circuit include the battery analyzer. 11.The system of claim 10, wherein the external system comprises apresentation device configured to present the measured battery statustrend and the calculated battery status trend.
 12. The system of claim11, wherein the presentation device comprises a screen adapted todisplay one or more of the measured battery status trend and thecalculated battery status trend.
 13. The system of claim 11, wherein thepresentation device comprises a printer adapted to print one or more ofthe measured battery status trend and the calculated battery statustrend.
 14. The system of claim 11, wherein the presentation devicecomprises an alarm device adapted to produce an alarm signal indicativeof a need for battery replacement.
 15. The system of claim 10, whereinthe implant battery monitoring circuit comprises the battery parametermonitor, the battery parameter calculator, and portions of the batteryanalyzer.
 16. The system of claim 10, wherein the implant batterymonitoring circuit comprises the battery parameter monitor, and theexternal battery monitoring circuit comprises the battery parametercalculator and the battery analyzer.
 17. The system of claim 16, whereinthe external battery monitoring circuit is configured to receive themeasured values of the battery functional parameter from each of aplurality of other implantable medical devices, and the battery analyzeris programmed to analyze the status of the battery using the measuredand calculated values of the battery functional parameter from theplurality of other implantable medical devices.
 18. The system of claim10, wherein the external system comprises an external devicecommunicatively coupled to the implantable medical device via atelemetry link, a telecommunication network, and a remote device adaptedto communicate with the external device through the telecommunicationnetwork.
 19. The system of claim 18, wherein external system comprises auser interface configured to present one or more of the measured batterystatus trend and the calculated battery status trend.
 20. The system ofclaim 19, wherein the remote device comprises a portion of the userinterface.
 21. A system for monitoring status of a battery in animplantable medical device, the system comprising: a battery analyzerconfigured to analyze the status of the battery, the battery analyzerincluding: a trending module including: a parameter input configured toreceive measured values of a battery functional parameter and calculatedvalues of the battery functional parameter, the battery functionalparameter indicative of a state of depletion of the battery, themeasured values each indicative of an actual state of depletion of thebattery, the calculated values each indicative of an expected state ofdepletion of the battery; and a processing circuit configured to producea measured battery status trend being a trend of the measured values ofthe battery functional parameter and a calculated battery status trendbeing a trend of the calculated values of the battery functionalparameter; and a trend alarm coupled to the trending module andconfigured to produce an alert signal when the measured battery statustrend deviates from the calculated battery status trend by at least aspecified performance margin for a monitoring period.
 22. The system ofclaim 21, wherein the trend alarm is configured to produce the alertsignal when a rate of change of the measured battery status trenddeviates from a rate of change of the calculated battery status trend byat least a specified performance rate margin for the monitoring period.23. The system of claim 21, comprising: a battery parameter monitorconfigured to measure the battery functional parameter and produce themeasured values of the battery functional parameter; and a batteryparameter calculator configured to produce the calculated values of thebattery functional parameter each as a function of one or morespecification parameters of the battery and one or more consumptionparameters indicative of energy consumption from the battery.
 24. Thesystem of claim 23, wherein the battery parameter monitor comprises aterminal voltage monitor configured to measure a terminal voltage beinga voltage across terminals of the battery.
 25. The system of claim 23,wherein the battery parameter monitor comprises a charging time monitorconfigured to measure a capacitor charging time being a time intervalduring which a capacitor in the implantable medical device is charged toa specified energy level using the battery.
 26. The system of claim 23,wherein the battery parameter monitor comprises a charge depletionmonitor configured to produce a charge depletion parameter indicative ofa cumulative charge depleted from the battery.